1. Field of the Invention
The present invention relates to a catalyst that is useful for oxidation, nitration, carboxylation, reactions for the formation of a carbon-carbon bond and other reactions, and to a process for producing an organic compound using the catalyst.
2. Description of the Related Art
An oxidation reaction is one of the most essential reactions in the field of organic chemical industry, and various oxidation processes have been developed. To save resources and to reduce environmental issues, catalytic oxidation processes using molecular oxygen or air directly as an oxidizing agent are preferred. However, such catalytic oxidation processes generally require high temperatures and/or high pressures for the activation of oxygen or, alternatively, must be performed in the co-existence of a reducing agent such as an aldehyde to proceed the reaction under mild conditions. Accordingly, these conventional catalytic oxidation processes cannot easily and efficiently produce alcohols or carboxylic acids under mild conditions.
Lower hydrocarbons such as methane and ethane are nitrated using nitric acid or nitrogen dioxide at high temperatures of from 250° C. to 300° C. However, when a hydrocarbon having a large number of carbon atoms is nitrated under the above condition, the substrate is decomposed, and a target nitro compound cannot be obtained in a high yield. To nitrate hydrocarbons, a method using mixed acid (a mixture of nitric acid and sulfuric acid) is widely employed. However, this method requires large amounts of strong acids in high concentrations.
Additionally, few processes are known for efficiently and directly introducing carboxyl groups into hydrocarbons under mild conditions.
Organic sulfur acids or salts thereof can be produced by various processes. For example, processes for producing a sulfonic acid include a process of oxidizing a thiol or disulfide with an oxidizing agent, a process of allowing an aromatic hydrocarbon to react with anhydrous SO3-pyridine or chlorosulfuric acid by using a Friedel-Crafts reaction, and a process of synthetically obtaining a sulfonic acid by subjecting an unsaturated compound to free-radical addition. These processes, however, require extreme reaction conditions or inevitably produce large amounts of by-products. Additionally, no processes for directly and efficiently sulfonating non-aromatic hydrocarbons have been known.
Some processes yield useful organic compounds by adding compounds to unsaturated compounds each having a carbon-carbon double bond or heteroatom-containing compounds. For example, by allowing an active methylene compound such as a malonic diester to react with an olefin having an electron attractive group, such as acrylonitrile, in the presence of a base, a carbon-carbon bond is formed as a result of a nucleophilic addition reaction and thereby yields an addition product (Michael addition reaction). By treating two types of carbonyl compounds in the presence of an acid or a base, one carbonyl compound is nucleophilically added to the other to form a carbon-carbon bond and thereby yields an aldol condensate.
These processes, however, are generally performed in the presence of an acid or base and cannot be applied to compounds each having a substituent that is susceptible to the acid or base. In addition, these processes cannot allow, for example, a hydroxymethyl group, an alkoxymethyl group, an acyl group or a tertiary carbon atom to directly combine with a carbon atom constituting an unsaturated bond of an unsaturated compound or with a methine carbon atom of a bridged cyclic compound.
Addition reactions to carbon-carbon double bonds in accordance with radical mechanisms or coupling reactions to form carbon-carbon bonds are also known. However, there are few processes that can efficiently yield addition or substitution reaction products or derivatives thereof by action of, for example, molecular oxygen under mild conditions.
Hydroxy-γ-butyrolactone derivatives can be produced by some processes. For example, European Patent Publication No. EP-A-2103686 discloses a process in which glyoxylic acid is allowed to react with isobutylene and thereby yields pantolactone. Likewise, Japanese Unexamined Patent Application Publication No. 61-282373 discloses a process in which hydrated glyoxylic acid is allowed to react with t-butyl alcohol and thereby yields pantolactone. Tetrahedron, 933 (1979) discloses a process for synthetically obtaining pantolactone. This process includes the steps of hydrolyzing 4-hydroxy-2-methyl-5,5,5-trichloro-1-pentene to yield 2-hydroxy-4-methyl-4-pentenoic acid and cyclizing this compound in the presence of hydrochloric acid. In addition, The Chemical Society of Japan, Spring Conference Proceedings II, pp. 1015 (1998) reports that light irradiation to a mixture containing an α-acetoxy-α,β-unsaturated carboxylic ester and 2-propanol yields a corresponding α-acetoxy-γ,γ-dimethyl-γ-butyrolactone derivative. However, these processes employ raw materials that are not easily available or require special conditions for the reactions.
Japanese Unexamined Patent Application Publications No. 8-38909 and No. 9-327626 propose oxidation catalysts each comprising an imide compound having a specific structure or the imide compound in combination with, for example, a transition metal compound. The catalysts are used for oxidizing an organic substrate with molecular oxygen. Japanese Unexamined Patent Application Publication No. 11-239730 discloses a process, in which a substrate is allowed to react with at least one reacting agent selected from (i) nitrogen oxides and (ii) mixtures of carbon monoxide and oxygen in the presence of the cyclic imide compound and thereby introduces at least one functional group selected from nitro group and carboxyl group into the substrate. PCT International Publication Number WO 00/35835 discloses a process, in which two compounds are allowed to react with each other in the presence of a specific imide compound and a radical generator with respect to the imide compound and thereby yield an addition or substitution reaction product or an oxidized product thereof in accordance with a radical mechanism. The processes using these imide compounds can introduce oxygen-atom-containing groups such as hydroxyl group, nitro group and carboxyl group into substrates or can form carbon-carbon bonds under relatively mild conditions. However, they are still insufficient in reaction rates or yields of the target compounds in reactions in the absence of solvents or in the presence of nonpolar solvents due to their low solubility in the reaction systems in question.